Alt() takes an alternating form

[RobinHankin]

Function Alt() is intended to take a tensor and return an alternating tensor. But it also takes a k-form, which can be confusing:

> Alt(rform())
A linear map from V^3 to R with V=R^7:
                  val
 6 1 4  =  -0.1666667
 6 7 2  =  -0.1666667
 3 6 1  =  -1.0000000
 7 2 6  =  -0.1666667
 [snip]

but right now I am not sure what the most desirable behaviour is.